1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device and in particular to a method of forming a silicon oxide film which is used as an interlayer insulating or dielectric film between wiring layers in the semiconductor device.
2. Disclosure of the Related Art
Recently, in semiconductor devices, two or more of metal wiring layers have been used for the purpose of high integration and speeding up thereof. As for an interlayer insulating or dielectric film between these metal wiring layers, in general a silicon oxide film has been used. In association with the requirements for highly densified or fine wiring layers and high aspect ratio, the insulating film having a smooth or planarized surface has been required to facilitate a processing step of the metal wiring in the subsequent steps.
In the past, as for a method of forming the silicon oxide film having such smooth surface, there have been known some methods as mentioned below.
As a first prior art, there was known, for instance, a method of forming a silicon oxide film in which a silicone film comprising siloxane having silicon and organic groups is applied on a semiconductor substrate and is subjected to plasma oxidation to form the silicon oxide film as taught in Japanese Unexamined Patent Publication Hei 1-130535. Namely, in this first prior art, a coating solution for forming the silicone based film is spin-coated on the semiconductor substrate and is dried at a temperature below 150.degree. C. to form the silicone based film. Successively, the semiconductor substrate is placed into an inductive coupling type plasma treating apparatus and is exposed to oxygen plasma to be oxidized by oxygen radicals, whereby the surface of the silicone based film is changed into a silicon oxide film.
As a second prior art, there was known a method of forming a silicon oxide film from tetramethylsilane and oxygen plasma as taught in S. Noguchi et al., Extended Abstracts of the 19th Conference on Solid State Devices and Materials, pp. 451-454 (1987). In the second prior art, a semiconductor substrate is placed in a reaction chamber, tetramethylsilane and afterglow of the oxygen plasma are introduced on the surface of the semiconductor substrate and subjected to reaction to thereby form a siloxane film having fluidity, typically a hexamethyldisiloxane film.
As a third prior art which is similar to the second prior art, there was known a method of forming a silicon oxide series film having fluidity by introducing silane and oxygen plasma onto the surface of a semiconductor substrate which was cooled to -110.degree. C. as taught in Extended Abstracts (The 38th Spring Meeting, 1991; The Japan Society of Applied Physics and Related Societies, p. 633.
As a fourth prior art, there was known a method of forming a siloxane film which comprises synthesizing siloxane from a tetraethoxysilane and water vapor system according to plasma-enhanced chemical vapor deposition, transporting the siloxane to the surface of a semiconductor substrate and forming the siloxane film thereon, as taught in M. Hatanaka et. al., Jun. 11-12, 1991 VMIC Conference, pp. 435-441.
Furthermore, as a fifth prior art, there was known a method of forming a silicon oxide film which comprises the steps of introducing plasma-enhanced silane gas onto the surface of a semiconductor substrate to adsorb silane radical (SiH.sub.x) to the semiconductor substrate surface and successively introducing plasma-enhanced oxygen gas onto the semiconductor substrate surface to oxidize the substrate surface with oxygen radical and form the silicon oxide film, one cycle consisting of the above two steps being repeated in the same apparatus to grow the silicon oxide film, as taught in M. Nakano et al., Extended Abstract of the 21st Conference on Solid State Devices and Materials, Tokyo, 1989, pp. 49-52.
In the case where the insulating films obtained by the above-mentioned prior arts are used as the interlayer insulating film between the metal wiring layers, various problems as mentioned below arise.
Application of the insulating film of the first prior art as the interlayer insulating film between the metal wiring layers will be explained with reference to FIGS. 1A to 1C.
As shown in FIG. 1A, a metal wiring layer 12 comprising Al or the like is formed on the surface of a semiconductor substrate 10 made of Si or the like through a silicon oxide film 11. Then, a silicone film 20 is deposited on the metal wiring layer 12 including the silicon oxide film 11 and thereafter the surface of the film 20 is subjected to inductive coupling type plasma treatment to change the surface into a modified silicon oxide film 21. Then, as shown in FIG. 1B, contact holes 23 are made at the designated place by a dry etching process to reach the surface of the metal wiring layer 12, in which a photoresist film 22 having openings at the designated position is used as a mask in the etching process. Thereafter, as shown in FIG. 1C, the photoresist film 22 is removed by oxygen plasma treatment. In this case, the surface of the silicone film 20 defining side walls of the contact holes 23 is oxidized by oxygen plasma to change to a low density silicon oxide film 24. Since this low density silicon oxide film 24 is highly hygroscopic, the film 24 absorbs atmospheric moisture. Thus, when the upper metal wiring layer or layers are formed, problems exist in that the metal wiring of the upper layer is broken and contact resistance increases because of outgas of the absorbed moisture.
In the second prior art, since the reaction of tetramethylsilane with oxygen is performed at a low temperature of -40.degree. C. to deposit the siloxane film, silicon oxide in the siloxane film is insufficiently bonded and thus the film becomes low density. If the siloxane film is used as the interlayer insulating film between the metal wiring layers, the siloxane film contracts during the subsequent heat treatment, for instance, at 400.degree. C. and thus cracks. A problem exists in that the cracking gives rise to the breaking and a short circuit of the metal wiring when the wiring layer is formed on the siloxane film.
Also, in the third and fourth prior arts, since the film deposition is performed at a low temperature, a problem exists in that the film cracks in the same manner as in the second prior art.
Furthermore, in the fifth prior art, since the silane radical has no fluidity, it is impossible to obtain the smooth surface. Also, since the afterglow of oxygen plasma is used in the oxidation reaction, gas molecule has low ion energy and the resulting silicon oxide film is a low density film. As a result, the silicon oxide film cracks during the subsequent heat treatment for densifying the film in the same manner as in the second prior art.